Pump for producing a vacuum free of hydrogen

ABSTRACT

A PUMP FOR PRODUCING A VACUUM FREE OF HYDROGEN COMPRISING AN INCANDESCENT FILAMENT FOR DISSOICATING HYDROGEN MOLECULARS INTO HYDROGEN ATOMS; AN OXIDIZING AGENT DISPOSED NEAR THE FILAMENT AND HAVING AT LEAST ITS SURFACE FORMED OF METAL OXIDES SO AS TO OXIDIZE MAINLY SAID DISSOCIATED HYDROGEN ATOMS INTO H2O; AND AN EXHAUST MEANS FOR DRAWING OUT VAPORS OF H2O PRODUCED ON SAID OXIDIZING AGENT.

Oct. 9, 1973 YOSHIO MURAKAMI PUMP FOR lRODUClNG A VACUUM FREE OF HYDROGEN 2 Sheets-Sheet 1.

Filed June 7,

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HYDROGEN PRESSURE (TOI'I) 9, 1973 Yosmo MURAKAMI 3,764,255

PUMP FOR PRODUCING A VACUUM FREE OF HYDROGEN 2 Sheets-Sheet 2 Filed June 7, 1971 INVENTOR.

Yvsb )0 Wav-dfiw/ BY United States Patent O PUMP FOR PRODUCING A VACUUM FREE OF HYDROGEN Yoshio Murakami, Yokohama, Japan, assignor to Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan Filed June 7, 1971, Ser. No. 150,656

Claims priority, application Japan, Dec. 11, 1970,

45/ 109,561 Int. Cl. B01d 53/00; F04b 37/00 US. Cl. 23252 R 9 Claims ABSTRACT OF THE DISCLOSURE A pump for producing a vacuum free of hydrogen comprising an incandescent filament for dissociating hydrogen molecules into hydrogen atoms; an oxidizing agent disposed near the filament and having at least its surface formed of metal oxides so as to oxidize mainly said dissociated hydrogen atoms into H and an exhaust means for drawing out vapors of H 0 produced on said oxidizing agent.

BACKGROUND OF THE INVENTION This invention relates to a pump and more particularly to a pump adapted to provide a vacuum free from hydrogen.

Vacuum pumps now in practical use include (1) Dynamic pumps such as rotary pumps, molecular pumps and diffusion pumps for exhausting gas molecules;

(2) Accumulation pumps such as getter pumps, cryogenic pumps and sorption pumps for adsorbing or condensing gas molecules to an adsorbent or a cold surface so as to remove them from the gaseous phase; and

(3) Ion pumps for exciting or ionizing gas molecules by energetic electrons so as to bury them into the surface layer of a material.

In recent years, however, there is growing demand in a certain industrial field for a special pump capable of selectively exhausting active gases, for example, hydrogen,

in high vacua. Since hydrogen molecules can easily backdiffuse from the foreside to the fine side in molecular pumps and diffusion pumps, and can not tightly bind to adsorbents or cold surfaces in accumulation pumps, there have heretofore been experienced great difliculties in its pumping. Therefore, the above-listed conventional vacuum pumps fail to draw out hydrogen gas fully and quickly.

SUMMARY OF THE INVENTION This invention has been accomplished in view of the aforesaid circumstances and is primarily intended to provide a pump capable of exhausting particularly hydrogen gas fully and quickly.

Namely, the pump of this invention comprises an incandescent filament for dissociating hydrogen molecules into hydrogen atoms; an oxidizing agent disposed near the filament and having at least its surface formed of metal oxides; and an exhaust means for removing vapors of H 0 obtained by the oxidation reaction on said oxidizing agent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a pump according to an embodiment of this invention;

FIG. 2 is a sectional view on line 11-11 of FIG. 1;

FIG. 3 is a curve diagram comparing the speed of the pump of the invention with those of the prior art pump;

FIG. 4 is a sectional view of a pump according to another embodiment of the invention; and

FIG. 5 is a fractional perspective view of a cooling bafiie used in the pump of FIG. 4.

3,764,266 Patented Oct. 9, 1973 DETAILED DESCRIPTION OF THE INVENTION There will now be described this invention by reference to the indicated embodiments. FIG. 1 shows an embodiment using a physical sorption pump as an exhaust means. Numeral 1 represents a pump casing which has an opening 2a at one end and is closed at the other and consists of a reactor 2 oxidizing hydrogen into water vapor and an exhaust means 3 branched off at right angles from the middle part of said reactor 2.

There will now be further detailed the reactor. There are sealed a pair of lead lines 4 into the reactor 2 from its closed end. Across the facing ends of said lead lines is stretched a hairpin-shaped tungsten filament 5. There is fitted by means of a support 7 a cylindrical copper shell 6 in a manner concentrically to surround said filament 5. A cuprous oxide layer of several microns thick is formed by anodic oxidation on the copper shell 6. The support 7 is also sealed into the reactor 2 from its closed end.

The exhaust means which is closed at the bottom comprises a cylindrical section 8 having an annular space 8a formed at the top; a cylindrical wire net 9 concentrically disposed in the cylindrical section 8; a porous adsorbent 10 consisting of, for example, synthetic zeolite, activated alumina or charcoal which is packed between the outer wall of the wire net 9 and the inner wall of the cylindrical section 8; and a heat insulation vessel 12 containing liquid nitrogen 1.1. for cooling said adsorbent 10. The aforementioned annular space 80. is poorly evacuated and contains a fully degassed porous adsorbent 13. The cylindrical section 8 is immersed in the liquid nitrogen 11 received in the heat insulation vessel 12, for example, a Dewar flask and has the part below the annular space 8a kept at low temperature. Further, for the conduction of heat through the porous adsorbent, there may be provided, as shown in FIG. 2, on the inner wall of the cylindrical section 8 a large number of metal plates 14, for example, copper plates directed toward the center of said section 8. Where there is to be adsorbed water vapor alone, the porous adsorbent is effective even at normal temperature, thus eliminating the necessity of installing said cooling means. However, adsorption of less adsorbable gases, for example, N 0 and CO requires the porous adsorbent to be cooled using liquid nitrogen.

The annular space 8a is so designed as to reduce a temperature gradient as much as possible in order to prevent certain gases from being released from or struck on the upper part of the exhaust means 3.

Where, under the aforementioned arangement, there is introduced current from the lead lines 4 to the filament 5 to heat it to around 2000 K., heating can be effected rapidly and instantly brought to a stable state. Under such condition, several or scores of percent of hydrogen molecules can be dissociated into hydrogen atoms on the surface of the incandescently heated filament 5. When the hydrogen atoms are brought to the surface of cuprous oxide, there occurs the following reaction:

The degree of the reaction (I) is almost unity regardless of temperature, offering far greater advantage than in the following reaction (II) where hydrogen molecules are oxidized on the surface of cuprous oxide.

In the latter case, the surface of cuprous oxide has to be heated to about 200 to 400 C. and yet reaction proceeds slowly. Further, Where hydrogen molecules are removed only by the reaction (II), gases are likely to be released from the oxide itself as well as from the walls of a vessel containing the same due to application of such high temperature, with the resultant increase in pressure.

Moreover, it is necessary to provide a rigid heat insulation plate between the oxidizing means and porous adsorbent, possibly leading to decrease in gas conductivity between the oxidation and adsorption sections.

The reaction of oxidizing hydrogen occurring in the pump of this invention depends to a far greater extent on the oxidation of hydrogen atoms H dissociated by the filament 5 on the surface of cuprous oxide supported on the cylindrical copper shell 6 than on the oxidation of hydrogen molecules H2 on said surface. Accordingly, the rate of total reaction is determined mainly by the surface area of the filament and the degree of dissociation of hydrogen molecules. Where the tungsten filament 5 is heated to 2000 K. according to this embodiment, said degree of dissociation for the range between 10- and 10- torr is 0.61.0, and can be further increased by heating the filament to higher temperatures.

When brought into contact with the surface of cuprous oxide, carbon monoxide can be converted to carbon dioxide by the following reaction formula:

Since carbon monoxide can thus be converted to easily adsorbable carbon dioxide, the pump of this invention has an increased capacity to exhaust carbon monoxide. For reference, gases and vapors ready to be adsorbed to synthetic zeolite are given below in the decreasing order, the gases included in parenthesis denoting those little adsorbable to synthetic zeolite:

H O CO CO N CH O Ar H Ne He) FIG. 3 is a curve diagram presenting the performance of a pump arranged as shown in FIG. 1 according to an embodiment of this invention in comparison with that of the prior art pump, with hydrogen pressure (torr) plotted on the abscissa and the pump speed for hydrogen (l./sec.) on the ordinate. The curve A represents the performance of the pump of FIG. 1, showing the pump speed for hydrogen as determined when the reactor 2 was 45 mm. in inner diameter, the cylindrical copper shell 6 was 40 mm. in both diameter and axial length, and the filament 5 was 0.25 mm. in diameter and 80 mm. in total length and heated to 2000 K. The curve B denotes the performance of a prior art pump indicating the pump speed for hydrogen as determined when there was not used the filament 5, but instead there was wound a tape heater about that part of the periphery of the reactor tube 2 which faced the cylindrical copper shell 6 to heat the shell 6 to 400 C. In the case of the curve B, there occurred not only decrease in the pump speed for hydrogen but also increase in residual gas pressure due to release of gases from the walls of said copper shell and envelope.

FIG. 4 illustrates the arrangement of a pump according to another embodiment of this invention. As in FIG. 1, the exhaust means consists of a physical sorption pump. There is provided a cylindrical stainless steel member which is closed at the bottom and fitted at the top with a flange 20a communicating with an evacuated volume and also contains, as in FIG. 1, a porous adsorbent 21 and wire net 22 at the lower part. Above the porous adsorbent 21 is disposed a cooling baffle 24 fitted with a large number of heat-radiating plates 23. To describe in detail, said cooling bafiie 24 consists of a hollow member 26 provided with an inlet tube 26a and outlet tube 26b of liquid nitrogen extending in opposite directions and the aforementioned heat-radiating plates 23 which are stretched across the opposite inner walls of the hallow member 26 and pointedly bent at the center in the same direction, that is, are arranged parallel with each other. As in FIG. 1, the lower half of the cylindrical member 20 for cooling the porous adsorbent 21 is immersed in liquid nitrogen 11 received in the heat insulation vessel 12. The outer walls of the lower half of the cylindrical member are wou d wi h a shea h heater 2.5 which, when h porous adsorbent 21 is saturated with water vapor, is so designed as to heat said adsorbent 21 for degassing of water vapor, thereby rendering it ready for reuse.

On the upper side wall of the cylindrical member 20 between the flange 20a and the cooling baffle 24 is provided a branched section 27 oxidizing hydrogen into water vapor extending at right angles from said upper side wall. In said branched section 27 are received an assembly type oxidant member 28 and a replaceable filament 29.

Said oxidant member 28 is constructed by laminating a plurality of annular surface-anodized copper plate units 28a with spacers 28b interposed therebetween and inserting support rods 30 and 31 through said units 28a and bolting them into an integral body. One support rod 30 is made longer than the other 31 and fitted at one end into the inner wall of a cap member 32 mounted on the flange 27a of the branched section 27 in airtight and detachable relationship. The filament 29 is so disposed as to penetrate the central opening of said annular copper plate units 28a and fitted to two support plates 33 and 34 with the oxidant member 28 disposed between the support rods 30 and 31. The support plate 33 facing the cylindrical member 20 is grounded therethrough and provided with a filament-supporting metal part 35 made electrically conducting and the other support plate 34 is fitted with a filament-supporting metal part 36 electrically insulated from the former metal 35. The cap member 32 has a terminal 37 penetrating therethrough in airtightness. The filament 29 is supplied with electric current through said terminal 37 and pump casing.

The pump according to the embodiment of FIG. 4 is adapted to treat a large capacity of hydrogen, though operated in the same manner as that of FIG. 1, and further offers great operating advantage because it permits easy replacement of both filament and oxidizing agent.

As mentioned above, the pump of this invention dissociates hydrogen molecules H into hydrogen atoms H by an incandescent filament and enables the hydrogen atoms to be oxidized on the surface of cuprous oxide with the degree of oxidizing reaction being unity regardless of temperature, thus eliminating the necessity of using cuprous oxide having a particularly large surface or heatng said surface to high temperatures. Accordingly, the invention is capable of evacuating hydrogen efficiently at a high rate and maintaining a low ultimate pressure.

The foregoing embodiments relate to the case where the oxidizing agent consisted of a surface-anodized copper shell or plate. However, this invention is not limited to said embodiments, but permits other types of oxidizing agent, for example, those prepared by coating the surface of other metal materials with powders of, for example, CuO or Cu O. Further, there may be used other oxidizing agents, for example, nickel oxide, iron oxide or cobalt oxide, provided their dissociation pressures and vapor pressures are low enough at operating temperatures. The filament may be formed of various materials such as tungsten, rhenium, platinum, and palladium which can Withstand temperatures of about 2000" K. The porous adsorbent may consist of not only zeolite, but also activated alumina or charcoal. When such porous adsorbent is saturated with Water vapor, it can be regenerated by being heated to a temperature of about 400 C. for degassing of the adsorbed water vapor wln'ch is pumped out by a supplementary pump. Where there is used a physical sorption pump as an exhaust means, the heating section of the reactor should be thermally insulated from the cooling section of a gas adsorbent. Further, the filament and oxidizing agent should be located near enough to each other to allow hydrogen atoms dissociated by the filament to travel straight to the oxidizing agent.

Where there is required a pump for selectively pumping mainly H or H O, it is possible either to adsorb only H O (including that kind of H 0 which is converted from H by maintaining the adsorbent used in the foreg ing m odimen s at normal t mp r ture, or to cool the pump casing with liquid nitrogen without using an adsorbent.

The exhaust means used in the pump of this invention is simply intended to remove water vapor generated by oxidation reaction. It will be apparent, therefore, that in addition to the physical sorption pump used in the aforementioned embodiment, there may be used conventional pumps such as ditfusion-, getter-, sputter ion-, and molecular pumps.

What is claimed is:

1. A pump for producing a vacuum substantially free of hydrogen which comprises:

an airtight vessel having an inlet thereto,

a filament formed of metal that can withstand temperatures of about 2000 K.,

electrical leads sealed into said airtight vessel on which said filament is mounted for electrical connection through said leads to an external source of electricity to heat said filament to an incandescent state capable of dissociating molecular hydrogen into atoms,

a layer of metal oxide selected from the group consisting of copper oxide, nickel oxide, iron oxide and cobalt oxide disposed near said filament, said oxide layer being capable of reacting with atomic hydrogen formed by said filament to produce water vapor, and

a trap for water vapor.

2. A pump as claimed in claim 1 wherein said layer of metal oxide is supported on a cylindrical shell concentrically surrounding said filament.

3. A pump as claimed in claim 1 wherein said layer of metal oxide consists of a plurality of annular plates bearing said metal oxide laminated together and said filament penetrates a central opening in the assembly of annular plates.

4. A pump as claimed in claim 1 wherein the metal oxide is cuprous oxide.

5. A pump as claimed in claim 1 wherein said trap is a liquid nitrogen cold trap.

6. A pump as claimed in claim 1 wherein said trap comprises a porous adsorbent.

7. The pump according to claim 1 wherein said trap comprises a physical sorption pump provided with an adsorption section containing a porous adsorbent and cooling means therefor.

8. The pump according to claim 7 wherein the physical sorption pump is provided with a cylindrical member disposed at a position substantially heat insulated from said oxidation reactor, synthetic zeolite received in said cylindrical member, a heater for heating said synthetic zeolite, and cooling means for cooling said synthetic zeolite.

9. The pump according to claim 1 wherein said trap comprises a physical sorption pump provided with a porous adsorbent, a means for cooling said adsorbent, and heat shielding plates disposed between the adsorbent and said filament.

- References Cited UNITED STATES PATENTS 3,149,775 9/1964 Pagano 417-48 3,172,745 3/1965 Needham et a1 4l748 1,970,700 8/1934 Kendall 23--284 2,582,885 1/1952 Rosenblatt 423-248 X 3,264,803 8/1966 Read 208 3,335,550 8/1967 Stern 55-208 3,658,485 4/1972 Gramer 23284 JOSEPH SCOVRONEK, Primary Examiner U.S. Cl. X.R. 

